These are the two main ways to mount a tool box to a pickup, and they suit genuinely different trucks. The choice is less about capacity than about which part of the bed you are willing to give up.
What Is the Difference?
A crossover box spans both bed rails just behind the cab, opening upward from the middle of the truck. A side mount box, usually called a lo-side or hi-side, runs lengthways along one rail and opens from the side of the vehicle. One takes the front of the bed, the other takes the length of a rail.
Crossover Boxes
The crossover is the default for good reason. It gives the largest single locked space, it uses a part of the bed that is awkward for cargo anyway and it fits without drilling. It is also the easiest to reach into from either side of the truck.
The cost is bed length. On a short bed, a full-depth crossover leaves very little usable floor, which is the reason low profile versions exist.
Crossovers also block the rear window on most trucks unless you choose a low profile or angled version. On a truck that reverses to a dock all day that is a real cost, and it is the complaint that comes up most often from people who bought on capacity alone.
Side Mount Boxes
Lo-side boxes sit below the rail line and hi-side boxes sit above it. Both run along the bed side, which leaves the front of the bed completely clear and keeps the rear window unobstructed.
- Lo-side: below the rail, keeps the bed opening clear from above.
- Hi-side: taller body, more capacity, sits proud of the rail.
- Both leave the bulkhead free for a rack, a tank or a second box.
- Both are sold per side, so a matched pair doubles storage.
Access Is the Everyday Difference
A side mount box opens toward you as you stand beside the truck, at roughly waist height, which makes it the more comfortable of the two for tools you reach for constantly. A crossover asks you to lean over the rail and reach down.
Against that, a crossover is reachable from either side of the truck. A lo-side box on the driver side means walking into the road to open it, which is worth thinking about for a truck that works on street jobs.
Running Both
They are not exclusive, and plenty of service trucks carry a crossover at the bulkhead and a lo-side down one rail. Together they cover both use cases: bulk storage at the front, everyday tools within reach at the side.
Compare crossover boxes against lo-side boxes and hi-side boxes, or see the full tool box range.